ISDN for Home or Business:  An Introduction and Brief Orientation
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Q.  What is ISDN?

A.  ISDN (Integrated Services Digital Network) is an international
standard for making digital telephone calls.  Using the telephone
network we all use today in the course of talking to friends and family
or for conducting business, you can make higher-quality voice calls,
connect to the Internet -- or do both, at the same time.  ISDN has been
in use around the world for years, but has only become popular in the
U.S. in the past two years. This popularity can be primarily attributed
to widespread demand for faster connections to the Internet.


Q:  Why is digital better?

A:  Today, nearly all voice communications are carried digitally after
they leave your telephone company's central office. For standard
telephone service, the only analog portion of the telephone network is
the link between the central office and you. ISDN replaces this analog
connection with digital service, resulting in greater service capacity,
and significantly higher quality.

Unlike plain old telephone service (POTS), ISDN is fully digital, thus
eliminating the need to take the digital data your computer generates
and turn them into analog tones or phase-shifts (those "whooshy" noises
you hear if you pick up an extension while a modem is operating).
This enables you to send data much more efficiently, and therefore
faster, over the same wires.


Q.  What do I need to change to use ISDN?

A.  Ordinary copper wires, probably the same ones you use today for your
conventional telephone service, bring the service into your business. 
To use ISDN for connecting a single computer to the Internet, or for making
ordinary voice calls, though, you need a special box, a kind of "digital
modem" called a terminal adapter.

If you have a LAN with a number of computers you'd like to connect to the
Internet, you can use a special type of terminal adapter generally called
an ISDN router.  This box combines the functions of an ISDN terminal adapter
with a router capable of managing a TCP/IP connection between your
LAN and Northwest Nexus.


Q.  How much data can an ISDN line carry?

A.  The ISDN service that individuals and businesses are most likely to
use provides two separate "channels" that can each carry data or voice
information.  Each of these "B" channels have a capacity of 64kb/s.   A
third channel (called "D") is used by the terminal adapter to establish
calls with the central office.

You can use one "B" channel to make a voice call while simultaneously
using the other "B" channel for an Internet connection to Northwest
Nexus. In some situations, you can use both "B" channels together,
effectively doubling the speed of your data connection to as much as
128kb/s.  And some terminal adapters let you make two voice calls at the
same time, one on each "B" channel.

You can have as many simultaneous connections as you have "B" channels:

	One voice, one data
	Two data
	Two voice


Q:  How fast is ISDN compared with my modem or with frame-relay service?

A:  Using a regular telephone line and standard V.34 (28.8k) modem, the
maximum data transmission speed is 28.8 kb/s (28,800 bits per second).
With an ISDN line and the proper equipment and system configuration,
your speed (throughput) can be as high as 128 kb/s (128,000 bits per
second) -- over four times faster.  This is substantially faster than
most of the sites on today's Internet can provide data.

Frame-relay service starts at a speed of 56kb/s; a single-channel ISDN
connection at 64k can be a third or more faster, due to differences in
the nature of the types of connection.  Two-channel connections at
128kb/s are not only faster than 128kb/s frame-relay, they're easier
and less expensive to install and maintain.   


Q:  Should I disconnect my primary telephone service when I order my ISDN
line?

The answer to this question for the majority of residential ISDN users
is "no."  If you are willing to take our word on this, you do not need to
spend any additional time deciphering the issues involved with primary
telephone service replacement.

Some ISDN terminal adapters provide telephone jacks into which you can
plug a standard telephone.  You can use this telephone to make and
receive telephone calls just like you use your regular telephone line.
Some adapters even include two of these jacks, and let you make and
receive two voice calls at once.

It would seem, then, that if you're happy with using a single 64kb/s "B"
channel for your Internet connection, you could use the other "B"
channel to provide your household or business telephone service. Indeed,
the writer of this FAQ does exactly this for his business telephone
service.

Before disconnecting your primary (analog) telephone service, consider
the following:
	
	- Long-distance rates for voice calls on ISDN lines can be higher.
	- Most ISDN terminal adapters do not work when AC power is out, which
	  means that your telephone won't work either.
	- Most terminal adapters are unable to supply sufficient power to make
	  more than a single telephone ring.

In general, one or more of these considerations make ISDN unsuitable for
replacing home telephone service.  In some business situations, however,
using ISDN to provide both Internet service and a business telephone
line may be financially attractive.


Q.  What kinds of Internet service are available via ISDN?

A.  Northwest Nexus currently provides three ISDN Internet services:

	- Dial-Up ISDN Service
	  Same as Premium Dial-Up Service, but delivered via ISDN.  This
	  is the type of service you can use to upgrade your current modem
	  connection to the Internet.

	- Dedicated ISDN 64kbps (one B-channel)
	- Dedicated ISDN 128kbps (two B-channels)
	  Suited for connecting a local LAN to the Internet, these services
	  are often used in place of frame-relay connections.
	
Additional services are currently in development; join our mailing lists
to be notified when these services are available (see below).


Q:  I'm still interested:  what do I do next?

A.  Obtain and review "Establishing ISDN Service with Northwest Nexus,"
the next FAQ in this series.  The complete set of ISDN FAQs includes the
following titles:

	ISDN for Home or Business:  An Introduction and Brief Orientation
		(the FAQ you are reading)
  	ISDN Glossary
    	(ISDN-related terms, acronyms and definitions)
	Establishing ISDN Service with Northwest Nexus
		(how to order, install ISDN service)
	Selecting an ISDN Terminal Adapter
		(how to select, overview on install and setup)
	Selecting an ISDN Router
		(how to select, overview on install and setup)
	Configuring Your ISDN Terminal Adapter
	Configuring Your ISDN Router
		(specifics on adapter configuration and software setup)
	Debugging ISDN 
	  (general debugging tips)





[1Apr97/MJT]